Stirring apparatus



May 1968 E. c. sue-sow ET L 3,381,941

STIRRING APPARATUS Filed Aug. 17, 1966 L T II United States Patent Office 3,381,941 Patented May 7, 1968 3,381,941 STIRRING APPARATUS Eugene C. Gibson, Havertown, and Otto K. Carlson, Marcus Hook, Pa., assignors to FMC Corporation, Philadelphia, Pa., a corporation of Delaware Filed Aug. 17, 1966, Ser. No. 573,056 3 Claims. (Cl. 259-108) ABSTRACT OF THE DISCLOSURE Stirring apparatus having parallel blades with each blade having end portions which are laterally offset with respect to each other. Linking means are connected to the otfset end portions of the blades to enable the blades to gradually move from a position adjacent the shaft of the stirrer to a fully extended position.

This invention relates to a stirring apparatus and partio ularly to an apparatus for stirring, mixing or blending a material which gradually changes from a low to a high viscosity.

In stirring a highly viscose material in a vessel, the drag of the vessel wall has a strong tendency to prevent that portion of the material in the vicinity of the Wall from moving and therefore it is desirable that the stirring apparatus should produce a scraping action against the vessel wall to continually force that portion of the material into circulation. In the case of a material having a low viscosity, movement of a stirrer element around the wall of the containing vessel produces a vortex action leaving a cavity or vacuum in the center of the vortex whereby good mixing is not obtained. Therefore, with a low viscosity material the stirrer element should rotate near the center of motion of the material whereby the material entering the center of the vortex immediately comes in contact with the stirrer and the usual cavity or vacuum is not permitted to form. By employing complex motions and varying speeds it is possible to obtain good mixing of a material which changes viscosity during the operation but if the stirrer is to have a simple rotary motion then the stirrer for the low viscosity stage of the material should normally have a different construction from the stirrer for the high viscosity stage.

It is an object of the present invention to provide an improved stirring apparatus having a simple rotary motion which will satisfactorily stir or mix materials of either a high or a low viscosity.

A more particular object of the invention is to provide a stirring apparatus rotating at constant speed which will satisfactorily stir a material which gradually undergoes a great change from a low to a high viscosity.

Other and further objects, features and advantages of the invention will become apparent as the description of a preferred embodiment thereof proceeds.

Referring now to the drawing:

FIG. 1 is a side elevational view of the stirrer portion of the apparatus;

FIG. 2 is a side elevational view taken at right angles to FIG. 1; and

FIG. 3 is a view partly in side elevation and partly in section of the entire apparatus.

The stirrer comprises a shaft 10, the lower portion of which may if desired have a square cross section. A stirrer blade 12 has pivotally connected thereto as by means of screws, bolts, pins or the like 14 and 16, a pair of parallel equal length links 18 and 20. As seen in FIG. 2, the ends of blade 12 are circumferentially displaced with respect to shaft and links 18 and 20 are pivotally connected respectively by screws, bolts, pins or the like 22 and 24 to circumferentially displaced portions of the shaft.

With this arrangement, blade 12 may move parallel to the shaft between a position adjacent the shaft as shown in full lines in FIG. 1 and a position remote from the shaft as shown in dotted lines in FIG. 1 and in full in FIG. 3. As will presently appear, the stirrer is intended to rotate about the longitudinal axis of shaft 10 and therefore in order to balance the structure a blade 26 similar to blade 12 is articulated to the shaft through links 28 and 30 which are pivotally connected to the shaft at positions diametrically opposed to the points of connection of links 18 and 20.

In use, that portion of the apparatus thus far described is located within a cylindrical walled vessel 32 with the axis of shaft 10 coincident with the central axis of the cylindrical wall of the vessel. The upper end of shaft 10 is suitably connected to a motor 34 which may be adjustably secured to a suitable support 36 whereby the stirrer may be moved into and out of the vessel as desired. The material to be stirred is indicated at 38 and shaft 10 is rotated in the direction such that the circumferential displacement of the ends of blade 12 and the similar displacement of the ends of blade 26 in cooperation with the material in the vessel tends to move the blades outwardly of the shaft. It is particularly apparent in FIG. 2 that rotation of the stirrer in the direction of the arrow will cause the material being stirred to exert an upward force component on blade 12.

Spring washers, one of which is indicated at 40, are provided for each of the bolts, screws or pins pivotally connecting the links to the blades 12 and 26 and to the shaft 10. These washers in cooperation with the heads of the bolts, screws or pins constitute adjustable friction means for retarding free swinging movement of the links. With only a light tension on the spring Washers, a very low viscosity material will not cause the blade 12 and 26 to move away from their positions adjacent shaft 10, but the force of a high viscosity material will. The tension on these washers may be adjusted for optimum movement of the blade depending upon the nature of the material being stirred.

.As previously indicated, the apparatus of this invention is primarily intended for stirring a material which starts out at a low viscosity and ends up at a great deal higher viscosity. For example, when changing cream to butter or making ice cream or even more noticably in certain polymerization processes such as making a polyester from ethylene gylcol and terephthalic acid. In these cases the operation is started with the blades in the inner position adjacent shaft 10 as shown in full lines in FIG. 1. The blades remain in this position as long as the viscosity remains low and they gradually move out as the viscosity is raised until they begin to scrape against the cylindrical wall of vessel 32 so as to bring that portion of the material adjacent the wall into circulation. Due to the varying locations of blades 12 and 26 there is no need to change the speed of shaft 10 in order to obtain a good mixing and stirring action. The apparatus may also be used for stirring a low viscosity material which remains at low viscosity and in this case the blades 12 and 26 remain adjacent shaft 10 during the entire operation. Also, the apparatus may be used with a high viscosity material in which case the blades immediately move to their outer position.

In some cases it may be desirable to provide a horizontal blade to scrape against the bottom and lower side portion of the vessel and such a blade is shown at 42 secured by a screw 44 to the bottom of shaft 10. The blades 12 and 26 when in their inner positions overlap op-pOsite side of blade 42 so that when they move to their outer positions there is only a small area of the cylindrical wall of the vessel which is not being scraped. This J1 unscraped area may be eliminated if desired by changing the length of links 18, 20, 2S, and 30 or by making the blade 42 higher than shown in the drawing.

Surrounding shaft 10 above the links 18 and 28 is an adjustable collar 46 which may be used to limit the outward swinging of links 18 and 28 and consequently the outward movement of blades 12 and 26 whereby the maximum pressure of the blades against the cylindrical wall of the vessel may be controlled.

Having thus described a preferred embodiment of the invention, what is claimed is:

1. Stirring apparatus comprising a shaft, a pair of equal length straight links pivotally connected at one end to longitudinally spaced and diametrically opposed points on said shaft, a stirrer blade having end portions which are laterally offset with respect to each other, means pivotally connecting one of said links to one of the end portions of said blade and means pivotally connecting the other of said links to the other end portion of said blade, said links being parallel to one another whereby said stirrer blade may move parallel to said shaft between a position adjacent said shaft and a position remote from said shaft.

2. The apparatus set forth in claim 1 comprising ad just able friction means for retarding free swinging movement of said links.

3. The apparatus set forth in claim 1 wherein said stirrer blade, said links and a portion of said shaft are located within a vessel having a cylindrical wall coaxial with said shaft, said links being of such length that said blade engages the cylindrical wall of the vessel when said blade is in the aforesaid position remote from said shaft, and means for rotating said shaft in the direction such that the circumferential displacement of the blade in cooperation with a material in the vessel tends to cause the blade to move from the position adjacent the shaft to a position remote from the shaft.

3/1919 Great Britain. 12/1920 Great Britain.

WILLIAM I. PRICE, Primary Examiner. 

